Modern semiconductor lasers are suitable as radiation sources in CW operation up to high modulation frequencies (several GHz).
CW semiconductor lasers are operated in such a manner that in the current radiation capacity characteristic curve of the laser, preferably above the threshold current I.sub.th, a certain DC operating point is set by a preliminary current I.sub.F. As required, a digital or HF signal is then modulated, or the laser is simply used as DC radiation source. In each case, it is necessary for various reasons (ageing, temperature dependence, etc.) to keep constant or stabilize the optical power of the laser.
A photodiode which is optically coupled to the laser radiation and is mostly arranged on the same base as the laser chip is primarily used for the stabilization. The photoelectric current of the photodiode, amplified via a control circuit, then controls the current I.sub.F of the laser in such a way as to keep the radiation capacity constant.